As known, the cabbage moth is a wide-spread pest, causing recurring damage in vegetables annually, primarily to cabbages and cauliflowers. Phosphoric acid esters were hitherto used to combat this pest; these compounds, however, do not exert a selective effect and are highly toxic to humans.
The problems of environmental pollution emerging in connection with the use of conventional pesticide chemicals can be eliminated for the Lepidoptera group when compositions containing the natural sex lures (sex pheromones) of the species to be combatted are used as insecticides. Sex pheromones are excreted by the females, and the males of the species can find the females to mate with them by the aid of the characteristic scent of the pheromone.
Pheromones can be used in plant protection in two ways. According to the first method, traps are baited with the sex pheromone and seize the male moths attracted by the active agents. In this way information can be obtained on the appearance of the pest, i.e. the prospective damage can be forecast. This method has the advantage over other forecasting methods utilizing traps that the pheromone-containing traps recover only the preselected pest, whereas light or UV devices trap practically all kinds of insects flying by night. Moreover, the pheromone-containing traps indicate the beginning of swarming generally more sensitively than do light traps [Mani et al: Schweiz. Z. Obst. Weinbau 81, 337-344 (1972)]. When the direct environment of the traps is treated with an insecticide, the majority of the male population attracted perishes in this killing zone, so that the risk of environmental pollution is restricted only to the killing zones, i.e. decreases to a considerable extent.
According to the second method, the so-called method of air permeation, the ability of males and females to find each other is distorted, thus their mating can be disrupted. In this instance a relatively greater amount of pheromone is emitted into the air over the plant culture to be protected, whereupon the males sense the presence of the pheromone everywhere. Thus they get confused and become unable to find the females. When pheromones are utilized according to this method, they are to be applied in far lower dosages than the classicial insecticides [W. L. Roefols and R. T. Carde: Ann. Rev. Entomol. 22, 377-405 (1977)].
The prior trapping technologies applied to protect plants against cabbage moths have the disadvantage that they cannot indicate the initial damage in due time; thus a protective treatment can be performed generally only when the elder caterpillars have already reached the internal parts of the plants and have become practically unavailable for the classical insecticides (e.g. phosphoric acid esters). When the sex pheromone of cabbage moths is applied in the trapping technique, this disadvantage can be eliminated.
Pheromones can also be used to advantage in the air-permeation technique since they are extremely selective and are nontoxic to vertebrates.
Szentesi et al [Act. Phytopath. Acad. Sci. Hung. 10, 425-429 (1975)] report on the extraction of the pheromone of cabbage moth, but they do not disclose the structure of the pheromone. Having isolated and analyzed this pheromone, Bestmann et al [Tetrahedron Letters 6, 605-608 (1978)] established that the multicomponent pheromone system of the cabbage moth contains (Z)-11-hexadecen yl acetate as the major component, they were not able to identify, however, possible minor components of the complex pheromone.
H. I. Bestmann et al [Chem. Ber. 111, 248-253 (1978)] also report on the synthesis of several 1-substituted-(Z)-11-alkenes, among others, (Z)-11-hexadecenyl acetate and (Z)-11-octadecenyl acetate.